Geomorphology of the slide, volume of material that slid into Lake Michigan,
loss of beach.

Summary

Conducted survey of subaerial and shallow water portions of the 1995
landslide to determine extent of sliding.

Notes

HELPING NPS UNDERSTAND LAKE MICHIGAN LANDSLIDE
Bruce Jaffe recently made the news in northern Michigan, where he is
studying a biglandslide that removed the beach along 500 m of shoreline in
Sleeping Bear Dunes National Lakeshore in February 1995. Approximately
100,000 cubic meters of sand above the shoreline of Lake Michigan and
1,000,000 cubic meters of sand below the shoreline slid into deep water
offshore, removing the beach and changing a gently sloping lake bottom into
a sharp 20-m dropoff near the shore. The National Park Service, concerned
about public safety and long-term effects on the coastal environment, asked
the USGS to study the slide. The request presents a unique opportunity to
Jaffe and his team, who conducted yearly topographic and bathymetric surveys
of the area from 1989 to 1993 as part of a shoreline-change study in the
Great Lakes Wetlands Project. With a detailed picture of pre-slide
conditions, they are well equipped to advance our understanding of coastal
and submarine landslides in lacustrine environments. The USGS team includes
Rob Kayen, Ken Israel, Tom Reiss, Homa Lee, Hank Chezar, and Guy Cochrane
from WUSGS and Randy Jibson from the Central Region Hazards Team. They are
receiving help from Max Holden of the Park Service and Jaques Locat of Laval
University, Quebec, Canada. The team has already begun conducting repeat
surveys of the area, using GPS and high-precision surveying equipment to
obtain elevations and positions accurate to within several centimeters. This
September they plan to (1) map the slide using 100-kHz sidescan sonar, (2)
conduct a bathymetric survey to quantify the volume of sediment moved during
the slide, (3) map sub-bottom lake geology using high-resolution seismic
reflection, and (4) deploy an underwater video camera to determine failure
type and slide-plane character. In FY97 they will install instruments to
measure geotechnical properties that could trigger sliding, and they will
perform a slope stability analysis to help the National Park Service predict
when the area may slide again. Two previous slides in this century--in 1913
and 1971- -indicate that landsliding will recur at the site. The team's work
was recently featured in front-page articles in two northern Michigan
newspapers, the Traverse City Record-Eagle (daily) and the Leelanau
Enterprise (weekly), and in a 10-minute National Public Radio broadcast
aired on local stations.